Process for preparing enantiomers of carbazole derivatives as 5-HT1 -like agonists

ABSTRACT

A (+) or (-) enantiomer of a compound of formula (I) wherein R 4  is methyl or ethyl, or a salt, solvate or hydrate thereof, processes for preparing said compounds and pharmaceutical compositions containing them. Compounds of formula (+) are 5-HT 1  -like agonists. ##STR1##

This is a divisional of application Ser. No. 08/446,655, filed Jul. 18,1995, now U.S. Pat. No. 5,618,947, which is a national phase applicationunder 371 of PCT application Ser. No. PCT/EP93/03627, filed Dec. 16,1993.

The present invention relates to certain tetrahydrocarbazolederivatives, in particular their enantiomeric forms, processes forpreparing them, pharmaceutical compositions containing them and theiruse in therapy, in particular the treatment of migraine.

International Patent Application WO93/00086 describes compounds of theformula: ##STR2## and salts thereof for use in the treatment ofconditions wherein a 5-HT₁ -like agonist is indicated, in particularmigraine.

In the above compounds R¹ represents hydrogen, halogen, trifluoromethyl,nitro, hydroxy, C₁₋₆ alkyl, C₁₋₆ alkoxy, arylC₁₋₆ alkoxy, --CO₂ R⁴,--(CH₂)_(n) CN, --(CH₂)_(n) CONR⁵ R⁶, --(CH₂)_(n) SO₂ NR⁵ R⁶, C₁₋₆alkanoylamino(CH₂)_(n), or C₁₋₆ alkylsulphonylamino(CH₂)_(n) ; R⁴represents hydrogen, C₁₋₆ alkyl or arylC₁₋₆ alkyl; R⁵ and R⁶ eachindependently represent hydrogen, or C₁₋₆ alkyl, or R⁵ and R⁶ togetherwith the nitrogen atom to which they are attached form a ring; nrepresents 0, 1 or 2; and R² and R³ each independently representhydrogen, C₁₋₆ alkyl or benzyl or together with the nitrogen atom towhich they are attached form a pyrrolidino, piperidino orhexahydroazepino ring. The carbon atom to which the group NR² R³ isattached (i.e. at position 3 of the tetrahydrocarbazole ring) is anasymmetric carbon atom and hence the compounds exist as optically activeenantiomers.

WO93/00086 describes inter alia the preparation of the above compoundswherein R¹ is --C(O)NH₂, one of R² and R³ is hydrogen and the other ismethyl or ethyl, viz:

6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole (as thehydrochloride salt) and

6-carboxamido-3-N-ethylamino-1,2,3,4-tetrahydrocarbazole (as the oxalatesalt). Both compounds were obtained only as mixtures of enantiomers.

We have now isolated the individual isomers of the above compounds.Thus, in a first aspect the present invention provides the (+) and (-)enantiomers of a compound of formula (I): ##STR3## wherein R¹ is methylor ethyl, or a salt thereof.

In accordance with convention the (+) and (-) designations indicate thedirection of rotation of plane-polarised light by the compounds. Theprefix (+) indicates that the isomer is dextrorotatory (also designatedd) and the prefix (-) indicates the levorotatory isomer (also designated1). The R and S designations denote the absolute configuration asdetermined by X-ray crystallography.

The individual compounds of formula (I) provided by the invention may benamed as:

R-(+)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole;(compound A)

S-(-)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole;(compound B)

R-(+)-6-carboxamido-3-N-ethylamino-1,2,3,4-tetrahydrocarbazole;(compound C)

S-(-)-6-carboxamido-3-N-ethylamino-1,2,3,4-tetrahydrocarbazole.(compound D)

Salts, solvates and hydrates of the above named compounds are alsowithin the scope of the present invention.

It will be appreciated that for use in medicine a physiologicallyacceptable salt should be employed. Suitable physiologically acceptablesalts will be apparent to those skilled in the art and include forexample acid addition salts such as those formed with inorganic acidse.g. hydrochloric, hydrobromic, sulphuric or phosphoric acids andorganic acids e.g. succinic, tartaric, malonic, citric, maleic, acetic,fumaric or methanesulphonic acid. Other non-physiologically acceptablesalts e.g. oxalates may be used for example in the isolation ofenantiomers of formula (I), and are included within the scope of thisinvention. Also included within the scope of the invention are solvatesand hydrates of enantiomers of formula (I) and their salts.

Acids which have more than one carboxyl group e.g. succinic, tartaric,malonic or citric acids may correspondingly react with more than onemolecule of an enantiomer (I), for example succinic acid may react witheither one or two molecules of (I) to form either a 1:1 salt (succinate)or a 2:1 salt (hemi-succinate). All such salt forms are encompassed bythe present invention; in general the 1:1 salt form is preferred.

Specific salts according to the present invention include:

(+)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole L(+)-tartrate salt (1:1),

(+)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole D(-)-tartrate salt (1:1),

(+)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazolehemisuccinate (2:1),

(+)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazolemethanesulphonate,

(+)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole succinate(1:1),

(+)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazolehydrochloride,

(+)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazolehydrobromide,

(+)-6-carboxamido-3-N-ethylamino-1,2,3,4-tetrahydrocarbazole succinate(1:1),

(+)-6-carboxamido-3-N-ethylamino-1,2,3,4-tetrahydrocarbazolehydrochloride, and

(+)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazolecamphorsulphonate.

It will be appreciated that an enantiomer according to the presentinvention for example a (+)-enantiomer, will be substantially free fromthe corresponding (-) enantiomer, and vice versa. Preferably, a specificenantiomer of the invention will contain less than 10%, e.g. less than5% and advantageously less than 1% e.g. less than 0.5% of its oppositeenantiomer.

In vitro testing (rabbit basilar artery) indicates that for both themethyl and ethyl derivatives of formula (I) the (+) enantiomer is moreactive than the corresponding (-) enantiomer. The above-named(+)-enantiomers are therefore preferred compounds of the invention.

Enantiomers of formula (I) may be prepared by standard methods, forexample:

(a) Separation of an enantiomeric mixture of a compound of formula (I)or a derivative thereof by chromatography e.g. on a chiral HPLC column.

(b) Separation of diastereoisomers of a chiral derivative (e.g. a chiralsalt) of a compound of formula (I) e.g. by crystallisation, or bychromatography.

(c) Alkylation of a (+) or (-) enantiomer of3-amino-6-carboxamido-1,2,3,4-tetrahydrocarbazole or a salt thereof,

followed if necessary or desired by converting a derivative of compound(I) so obtained into a compound of formula (I) itself or a differentderivative thereof e.g. by removal of any N-protecting group orfacilitating group, conversion of a salt into the free base, and/or saltformation.

Separation according to process (a) is generally facilitated by firstintroducing a readily removable group into the alkylamino moiety of thecompound of formula (I). Suitable removable facilitating groups includethose commonly used as N-protecting groups e.g. an alkoxycarbonyl groupsuch as t-butyloxycarbonyl or an aralkoxycarbonyl group such asbenzyloxycarbonyl, which groups may be introduced by reaction with forexample a di-alkyl-dicarbonate such as di-t-butyl-dicarbonate or achloroformate such as benzylchloroformate. The resulting enantiomericmixture can be applied to a chiral HPLC column and fractions containingthe individual isomers collected. A facilitating group may be removed bystandard methods such as acid hydrolysis or catalytic hydrogenation.

A chiral derivative according to process (b) is a derivative containingat least two chiral centres, such that an enantiomeric mixture of acompound (I) is converted into a pair of diastereoisomers. Suchderivatives include chiral salts wherein the anion contains a chiralcentre and derivatives of formula (I) in which the alkylamino moiety issubstituted by a group containing a chiral centre.

A chiral salt may be prepared for example by reaction of an enantiomericmixture, such as a 1:1 racemate, of a compound (I) with an opticallyactive acid such as (1S)-(+)-camphorsulphonic acid, d-tartaric acid,1-malic acid, 1-mandelic acid, 1-gulonic acid,2,3:4,6-di-O-isopropylidene-2-keto-L-gulonic acid orR-2-pyrrolidone-5-carboxylic acid (also known as D-pyroglutamic acid) togive two diastereoisomeric salts which may be separated e.g. bycrystallisation. The free base form of the desired enantiomer may beobtained by neutralisation with a base such as sodium hydroxide or anion exchange resin. Preferred optically active acids for use in thisprocess include (1S)-(+)-camphorsulphonic acid and especiallyR-2-pyrrolidone-5-carboxylic acid.

Alternatively, an optically active reagent such asR-α-methylbenzyloxy-succinimidate may be reacted with an enantiomericmixture of formula (I), to give a mixture of diastereoisomers which canbe separated by chromatography, followed by hydrogenolysis to give thedesired enantiomer of formula (I).

A chiral derivative may also be prepared by employing a chiral auxiliaryat an earlier stage in the synthesis as described hereinafter. This mayadvantageously result in a mixture enriched with one diastereoisomer ofa compound (I), and most preferably a single diastereoisomer, thusproviding a stereoselective synthesis of an enantiomer according to theinvention.

Alkylation of an enantiomer of3-amino-6-carboxamido-1,2,3,4-tetrahydrocarbazole according to process(c) may be carried out by standard methods well known in the art. Forexample alkylation may be achieved indirectly by formation of a groupwhich can be reduced to the desired alkylamino function (reductivealkylation). Thus for example the 3-amino compound can be reacted withan appropriate aldehyde or ketone e.g. formaldehyde, acetaldehyde oracetone, in the presence of a suitable reducing agent such as an alkalimetal borohydride or cyanoborohydride e.g. sodium cyanoborohydride.Alternatively formylation may be effected using p-nitrophenol formate inaqueous tetrahydrofuran, using similar reducing conditions. Preferably,the 3-amino compound is first reacted with benzaldehyde, also in thepresence of a reducing agent such as a cyanoborohydride, to form3-N-benzylamino-6-carboxamido-1,2,3,4-tetrahydrocarbazole, prior tointroduction of the methyl or ethyl group. The benzyl group maysubsequently be cleaved by standard methods such as catalytichydrogenation.

In a further alkylation method, an N-methyl substituent may beintroduced by formation of a 3-isothiocyanato derivative e.g. byreaction of the 3-amino compound with carbon disulphide anddicyclohexylcarbodiimide; followed by reduction for example with aborohydride.

It will be appreciated by those skilled in the art that other standardmeans of alkylation may also be employed.

The starting compounds for use in the above processes may be prepared bymethods known in the art for the preparation of tetrahydrocarbazoles,such as the methods described in International Application WO93/00086.Thus for example an enantiomeric mixture of formula (I) may be preparedby reductive alkylation of the corresponding 3-amino compound, asdescribed for process (c) above.

An enantiomeric mixture of formula (I) may also be prepared by reactionof 4-carboxamido-phenylhydrazine, or a salt thereof e.g. thehydrochloride, with 4-(methyl or ethyl)-aminocyclohexanone. In aparticular embodiment of this method a protected derivative of the4-alkylaminocyclohexanone is advantageously employed, e.g. a ketal offormula (II): ##STR4## wherein R¹ is as defined for formula (I), R² ishydrogen or an N-protecting group and A is an alkylene moiety, such asethylene or neopentylene (--CH₂ C(CH₃)₂ CH₂ --).

Compounds of formula (II) may themselves be prepared from a protected1,4-cyclohexane-dione of formula (III): ##STR5## by reaction with theappropriate alkylamine compound. This reaction may be effected in asuitable solvent, for example a hydrocarbon such as benzene or toluenein the presence of titanium tetrachloride or suitable molecular sievese.g. 4 Å molecular sieves, to give the corresponding iminoketalderivative which may then be converted to an alkylamino compound offormula (II) by catalytic hydrogenation using for example palladium oncarbon. Alternatively the reaction may be effected in a solvent such asan alcohol e.g. ethanol and the mixture hydrogenated directly, usinge.g. palladium on charcoal, to give a compound of formula (II).

The alkylamino group in the resulting compound of formula (II) may ifdesired be protected using standard methods. Suitable N-protectinggroups are well-known in the art and include for example acyl groupssuch as acetyl, trifluoroacetyl, or benzoyl; an alkyl- oraralkyloxycarbonyl group such as methoxycarbonyl, t-butoxycarbonyl,benzyloxycarbonyl or phthaloyl; and aralkyl groups such as benzyl,diphenylmethyl or triphenylmethyl. The protecting groups should beeasily removable at the end of the reaction sequence. N-deprotection maybe effected by conventional methods, for example an alkoxycarbonyl groupsuch as t-butoxycarbonyl may be cleaved by hydrolysis and anaralkyloxycarbonyl group such as benzyloxycarbonyl or an aralkyl groupsuch as benzyl may be cleaved by hydrogenolysis.

Cyclisation with 4-carboxamidophenylhydrazine or a salt thereof ispreferably carried out with a ketal of formula (II); however if desiredthe ketal may be converted to the corresponding ketone prior to thisreaction.

Yet a further method for preparing an enantiomeric mixture of formula(I) conlprises reacting a compound of formula (IV): ##STR6## wherein Zis a leaving group, such as a halogen atom or a sulphonyloxy (e.g.p-toluenesulphonyloxy or methanesulphonyloxy) group with an amine H₂ NR¹or a derivative thereof. Said derivative may optionally contain a chiralcentre, as in for example R-α-methylbenzylamine, resulting in adiastereoisomeric mixture of the corresponding derivative of formula(I). The diastereoisomers may be separated by chromatography, followedby hydrogenolysis to give the desired enantiomer of formula (I).

An enantiomeric mixture of3-amino-6-carboxamido-1,2,3,4-tetrahydrocarbazole may be prepared in ananalogous manner to formula (I), using 4-aminocyclohexanone, optionallyprotected as a ketal derivative, or an N-protected (e.g. phthalimido)derivative thereof. The enantiomers of3-amino-6-carboxamido-1,2,3,4-tetrahydrocarbazole may be resolved bychiral HPLC as described for process (a) above, using a derivative suchas of3-t-butyloxycarbonylamino-6-carboxamido-1,2,3,4-tetrahydrocarbazolc; orby formation of a chiral salt of the 3-arnino compound in a similarmanner to process (b) above, using for example2,3-4,6-di-O-isopropylidene-2-keto-L-gulonic acid, followed by selectivecrystallisation. Such methods are described in International ApplicationWO93/00086.

Enantiomers of formula (I) have been found to be agonists and partialagonists at 5-HT₁ -like receptors. Nomenclature of 5-HT receptors isconstantly evolving. At least four subtypes of the 5-HT₁ receptor familyhave been described, namely 5-HT_(1a), 5-HT_(1b), 5-HT_(1c) and5-HT_(1d). Functional contractile 5-HT₁ -like receptors have beenidentified in the dog saphenous vein and in cerebral (basilar) arteriesof various species including rabbit and human. It is now believed thatthe functional 5-HT₁ -like receptor correlates with the 5-HT_(1d)binding site (A. A Parsons, TIPS, Aug 1991, Vol 12).

Enantiomers of formula (I) are expected to have utility in the treatmentand/or prophylaxis of migraine, with and without aura, tension headache,cluster headache and other forms of cephalic pain and trigeminalneuralgias.

The invention therefore further provides the use of an enantiomer offormula (I) or a physiologically acceptable salt thereof in themanufacture of a medicament for the treatment of a condition where a5-HT₁ -like agonist is indicated, in particular the treatment orprophylaxis of migraine.

The invention also provides a method of treatment of a condition whereina 5-HT₁ -like agonist is indicated, in particular migraine, whichcomprises administering to a subject in need thereof an effective amountof an enantiomer of formula (I) or a physiologically acceptable saltthereof.

For use in medicine, a compound of the present invention will usually beadministered as a standard pharmaceutical composition. The presentinvention therefore provides in a further aspect pharmaceuticalcompositions comprising an enantiomer of formula (I) or aphysiologically acceptable salt thereof and a physiologically acceptablecarrier.

The compounds of formula (I) may be administered by any convenientmethod, for example by oral, parenteral, buccal, sublingual, nasal,rectal or transdermal administration and the pharmaceutical compositionsadapted accordingly.

The compounds of formula (I) and their physiologically acceptable saltswhich are active when given orally can be formulated as liquids orsolids, for example syrups, suspensions or emulsions, tablets, capsulesand lozenges.

A liquid formulation will generally consist of a suspension or solutionof the compound or physiologically acceptable salt in a suitable liquidcarrier(s) for example an aqueous solvent such as water, ethanol orglycerine, or a non-aqueous solvent, such as polyethylene glycol or anoil. The formulation may also contain a suspending agent, preservative,flavouring or colouring agent.

A composition in the form of a tablet can be prepared using any suitablepharmaceutical carrier(s) routinely used for preparing solidformulations. Examples of such carriers include magnesium stearate,starch, lactose, sucrose and cellulose.

A composition in the form of a capsule can be prepared using routineencapsulation procedures. For example, pellets containing the activeingredient can be prepared using standard carriers and then filled intoa hard gelatin capsule; alternatively, a dispersion or suspension can beprepared using any suitable pharmaceutical carrier(s), for exampleaqueous gums, celluloses, silicates or oils and the dispersion orsuspension then filled into a soft gelatin capsule.

Typical parenteral compositions consist of a solution or suspension ofthe compound or physiologically acceptable salt in a sterile aqueouscarrier or parenterally acceptable oil, for example polyethylene glycol,polyvinyl pyrrolidone, lecithin, arachis oil or sesame oil.Alternatively, the solution can be lyophilised and then reconstitutedwith a suitable solvent just prior to administration.

Compositions for nasal administration may conveniently be formulated asaerosols, drops, gels and powders. Aerosol formulations typicallycomprise a solution or fine suspension of the active substance in aphysiologically acceptable aqueous or non-aqueous solvent and areusually presented in single or multidose quantities in sterile form in asealed container, which can take the form of a cartridge or refill foruse with an atomising device. Alternatively the sealed container may bea unitary dispensing device such as a single dose nasal inhaler or anaerosol dispenser fitted with a metering valve which is intended fordisposal once the contents of the container have been exhausted. Wherethe dosage form comprises an aerosol dispenser, it will contain apropellant which can be a compressed gas such as compressed air or anorganic propellant such as a fluoro-chlorohydrocarbon. The aerosoldosage forms can also take the form of a pump-atomiser.

Compositions suitable for buccal or sublingual administration includetablets, lozenges and pastilles, wherein the active ingredient isformulated with a carrier such as sugar and acacia, tragacanth, orgelatin and glycerin.

Compositions for rectal administration are conveniently in the form ofsuppositories containing a conventional suppository base such as cocoabutter.

Compositions suitable for transdermal administration include ointments,gels and patches.

Preferably the composition is in unit dose form such as a tablet,capsule or ampoule.

Each dosage unit for oral administration contains preferably from 1 to250 mg (and for parenteral administration contains preferably from 0.1to 25 mg) of a compound of the formula (I) or a physiologicallyacceptable salt thereof calculated as the free base.

The physiologically acceptable compounds of the invention will normallybe administered in a daily dosage regimen (for an adult patient) of, forexample, an oral dose of between 1 mg and 500 mg, preferably between 10mg and 400 mg, e.g. between 10 and 250 mg or an intravenous,subcutaneous, or intramuscular dose of between 0.1 mg and 100 mg,preferably between 0.1 mg and 50 mg, e.g. between 1 and 25 mg of thecompound of the formula (I) or a physiologically acceptable salt thereofcalculated as the free base, the compound being administered 1 to 4times per day. Suitably the compounds will be administered for a periodof continuous therapy, for example for a week or more.

BIOLOGICAL TEST METHODS 5-HT₁ -like Receptor Screen

RABBIT BASILAR ARTERY

Experiments were performed in intracranial arteries from rabbit isolatedbasilar artery in a similar method to that described previously (Parsonsand Whalley, 1989. Eur J Pharmacol 174, 189-196.).

In brief, rabbits were killed by overdose with anaesthetic (sodiumpentobarbitone). The whole brain was quickly removed and immersed in icecold modified Kreb's solution and the basilar artery removed with theaid of a dissecting microscope. The Krebs solution was of the followingcomposition (mM) Na⁺ (120); K⁺ (5); Ca²⁺ (2.25); Mg²⁺ (0.5); Cl⁻ (98.5);SO₄ ²⁻ (1); EDTA (0.04), equilibrated with 95% O₂ /5% CO₂. Theendothelium was removed by a gentle rubbing of the lumen with a finemetal wire. Arteries were then cut into ring segments (ca 4-5 mm wide)and set up for recording of isometric tension in 50 ml tissue baths inmodified Krebs solution with the additional supplement of (mM); Na²⁺(20); fumarate (10); pyruvate (5); L-glutamate (5) and glucose (10). Thearteries were then placed under a resting force of 3-4 mN maintained at37° C. and the solution bubbled with 95% O₂ /5% CO₂.

After tests for initial reactivity with 90 mM KCl depolarising solutionand for lack of acetylcholine-induced relaxation of 5-HT (10 mM)precontraction, cumulative concentration-effect curves (2 nM-60 mM) to5-HT were constructed in the presence of ascorbate 200 mM, cocaine 6 mM,indomethacin 2.8 mM, ketanserin 1 mM and prazosin 1 mM.

Following a 45-60 min wash period, cumulative concentration-effectcurves to the test compounds or 5-HT (as a time match control) wereconstructed in the presence of ascorbate, indomethacin, cocaine,ketanserin and prazosin.

Test Compounds:

R-(+)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole;(compound A)

S-(-)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole;(compound B)

R-(+)-6-carboxamido-3-N-ethylamino-1,2,3,4-tetrahydrocarbazole;(compound C)

S-(-)-6-carboxamido-3-N-ethylamino-1,2,3,4-tetrahydrocarbazole.(compound D)

    ______________________________________    Results               EC.sub.50    ______________________________________    Compound A            0.03 μM    Compound B            >2 μM    Compound C            0.16 μM    Compound D            2.1 μM    ______________________________________

Pharmaceutical Formulations

The following represent typical pharmaceutical formulations according tothe present invention, which may be prepared using standard methods.

    ______________________________________    IV Infusion    Compound of formula (I)                           1-40 mg    Buffer                 to pH ca 7    Solvent/complexing agent                           to 100 ml    Bolus Injection    Compound of formula (I)                           1-40 mg    Buffer                 to pH ca 7    Co-Solvent             to 5 ml    ______________________________________

Buffer: Suitable buffers include citrate, phosphate, sodiumhydroxide/hydrochloric acid.

Solvent: Typically water but may also include cyclodextrins (1-100 mg)and co-solvents such as propylene glycol, polyethylene glycol andalcohol.

    ______________________________________    Tablet    ______________________________________    Compound             1-40 mg    Diluent/Filler*      50-250 mg    Binder               5-25 mg    Disentegrant*        5-50 mg    Lubricant            1-5 mg    Cyclodextrin         1-100 mg    ______________________________________     *may also include cyclodextrins

Diluent: e.g. Microcrystalline cellulose, lactose, starch

Binder: e.g. Polyvinylpyrrolidone, hydroxypropymethylcellulose

Disintegrant: e.g. Sodium starch glycollate, crospovidone

Lubricant: e.g. Magnesium stearate, sodium stearyl fumarate.

    ______________________________________    Oral Suspension    ______________________________________    Compound             1-40 mg    Suspending Agent     0.1-10 mg    Diluent              20-60 mg    Preservative         0.01-1.0 mg    Buffer               to pH ca 5-8    Co-solvent           0-40 mg    Flavour              0.01-1.0 mg    Colourant            0.001-0.1 mg    ______________________________________

Suspending agent: e.g. Xanthan gum, microcrystalline cellulose

Diluent: e.g. sorbitol solution, typically water

Preservative: e.g. sodium benzoate

Buffer: e.g. citrate

Co-solvent: e.g. alcohol, propylene glycol, polyethylene glycol,cyclodextrin

Preparation 1

(±)-3-Amino-6-carboxamido-1,2,3,4-tetrahydrocarbazole

4-Carboxamidophenylhydrazine hydrochloride (2.87 g) and4-phthalimidocyclohexanone (3.00 g) were mixed in acetic acid and themixture was heated under reflux for 2 hr. After cooling, the mixture wasneutralized using aq. potassium carbonate solution, and the yellow solidthus obtained was filtered, washed with water, and dried. Purificationby column chromatography (SiO₂ ; CHCl₃ /CH₃ OH) gave6-carboxarnido-3-phthalimido-1,2,3,4-tetrahydrocarbazole (2.8 g).

The above product (1.0 g) was suspended in ethanol (10 ml) and hydrazinehydrate (5 ml) was added. A clear solution was obtained, and the mixturewas left to stir overnight, to yield a precipitate. The whole mixturewas evaporated to dryness, washed with aq. K₂ CO₃ solution, and water,to leave the title compound3-amino-6-carboxamido-1,2,3,4-tetrahydrocarbazole (0.44 g), as themonohydrate, mp. 146-148° C.

¹ H NMR 250 MHz, DMSO-d⁶ !δ 1.49-1.77 (1H,m), 1.83-2.03 (1H,m),2.17-2.40 (1H,m), 2.62-2.80 (2 H,m), 2.90 (1H,dd), 1 signal obscured byH₂ O at ca. 3.1, 7.03 (1H,brd.s), 7.18 (1H,d), 7.58 (1H,d), 7.83(1H,brd.s), 7.98 (1H,s).

Preparation 2

(+)- and (-)-3-Amino-6-carboxamido-1,2,3,4-tetrahydrocarbazolehydrochloride

Method 1

(±)-3-t-Butyloxycarbonylamino-6-carboxamido-1,2,3,4-tetrahydrocarbazolewas separated into its enantiomers using chiral HPLC: (chiralcel OD 4.6mm column, eluting with hexane/ethanol 85:15). The (+)-enantiomer wascollected first and had mp=150-152° C. and α!_(D) ²⁵ =+70.1 (inmethanol, 0.41% w/v). The (-)-enantiomer had mp=150-152° C. and α!_(D)²⁵ =-79.4 (in methanol, 0.40% w/v). The (+)-enantiomer was converted tothe parent amine hydrochloride by treating with HCl gas in dioxane, tofurnish the (+)-enantiomer of3-amino-6-carboxamido-1,2,3,4-tetrahydrocarbazole hydrochloride,mp=248-251° C., α!_(D) ²⁵ =+26.2 (in methanol, 0.50% w/v). The(-)-enantiomer of3-t-butyloxycarbonylamino-6-carboxamido-1,2,3,4-tetrahydrocarbazole wassimilarly converted into the (-)-enantiomer of3-amino-6-carboxamido-1,2,3,4-tetrahydrocarbazole hydrochloride,mp=248-251° C., α!_(D) ²⁵ =-28.6 (in methanol, 0.50% w/v).

Method 2

(±)-3-amino-6-carboxamido-1,2,3,4-tetrahydrocarbazole was treated withone equivalent of 2,3:4,6-di-O-isopropylidene-2-keto-L-gulonic acid inmethanol to give the salt of the (+)-enantiomer, in 38% yield (withrespect to racemate) and 84% enantiomeric excess (ee). This material wasrecrystallized twice from methanol to give the salt of the(+)-enantiomer in 25% overall yield (with respect to racemate), and >98%ee. This product was converted to the hydrochloride salt first bytreatment with aqueous alkali, and the precipitated free base treatedwith 2M aq. HCl in ethanol, to give(+)-3-amino-6-carboxamido-1,2,3,4-tetrahydrocarbazole hydrochloride.

Preparation 3

(±)-6-Carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazolehydrochloride

4-Cyanophenyl hydrazine hydrochloride (20.2 g) and4-benzoyloxy-cyclohexane (25.9 g) were dissolved in glacial acetic acid(400 ml) and the mixture was heated under reflux for 1.5 hr. Afterallowing to cool, the mixture was filtered, and the filtrate wasevaporated to dryness, and neutralized with aqueous sodium bicarbonatesolution to give a solid precipitate, which was purified bychromatography (SiO₂ ; hexane/ethyl acetate) to give3-benzoyloxy-6-cyano-1,2,3,4-tetrahydrocarbazole (18 g). This product(11.6 g) was suspended in ethanol (230 ml) and treated with 2.5% aqueouspotassium hydroxide solution (120 ml), and heated under reflux for 1 hr.The cooled mixture was neutralized with glacial acetic acid andevaporated to a solid residue which was washed with water, and dried togive 3-hydroxy-6-cyano-1,2,3,4-tetrahydrocarbazole (6.6 g).

The above product (3.57 g) was dissolved in dry pyridine (35 ml) andtreated with tosyl chloride (3.51 g) in dry pyridine (35 ml), and themixture was stirred at 100° C. for 2 hr. After cooling, the solution waspoured into water (500 ml), extracted with ethyl acetate, and the latterextract was washed with 2M HCl, dried (MgSO₄) and evaporated to dryness.Purification by chromatography (SiO₂ ; hexane/ethyl acetate) gave3-tosyloxy-6-cyano-1,2,3,4-tetrahydrocarbazole (0.53 g).

This product (0.40 g) was dissolved in 33% methylamine in alcohol (25ml) and heated at 100° C. in a sealed steel vessel for 1.5 hr. Aftercooling, the mixture was evaporated to dryness and purified bychromatography (SiO₂ ; chloroform/methanol) to give3-methylamino-6-cyano-1,2,3,4-tetrahydrocarbazole (0.13 g).

The above product (0.12 g) was dissolved in THF (10 ml) and reacted withdi-tert-butyl dicarbonate (0.36 g) in THF (3 ml) at room temperatureovernight. The reaction mixture was evaporated to dryness, partitionedbetween 2M sodium bicarbonate solution and ethyl acetate, and theorganic extract dried and evaporated to give a white solid. This wastriturated with ether/hexane to give3-t-butyloxycarbonylmethylamino-6-cyano-1,2,3,4-tetrahydrocarbazole(0.14 g).

This product (0.14 g) was dissolved in methanol (15 ml) and treated witha mixture of 20% aqueous sodium hydroxide (0.20 ml) and 30% hydrogenperoxide (0.20 ml), and the whole mixture was stirred at roomtemperature overnight. Sodium metabisulphite (38 mg) was added, and thesolution was evaporated to dryness, and chromatographed (SiO₂ ;chloroform/10% NH₄ OH in methanol) to give3-methylamino-6-carboxamido-1,2,3,4-tetrahydrocarbazole (0.12 g). Theabove compound (0.11 g) was dissolved in methanol (10 ml), and treatedwith 3M hydrochloric acid at room temperature. The mixture wasevaporated to dryness, azeotroping with ethanol to give a solid, whichwas recrystallized from methanol/ether to give the title compound, mp327-328° C. (80 mg).

1H NMR 250 MHz, MeOH-d⁴ ! d 1.98-2.20 (1H, m), 2.29-2.49 (1H, m),2.75-2.90 (5H, s+m), 2.90-3.09 (2H, m), 3.52-3.69 (1H, m), 7.31 (1H, d),7.63 (1H, d), 8.05 (1H, s).

Preparation 4

(±)-6-Carboxamido-3-N-ethylamino-1,2,3,4-tetrahydrocarbazole oxalate

1,4-Cyclohexanedione mono-2',2'-dimethyl trimethylene ketal (2.00 g) wasmixed with anhydrous ethylamine (10.0 g) and benzene (10 ml), and themixture was cooled to 5° C. A solution of titanium tetrachloride (0.95g) in benzene (10 ml) was added, dropwise, then the mixture was stirredat room temperature for 1 hr. The mixture was filtered, and evaporatedto dryness to give an oil, which was dissolved in ethanol (30 ml). Tothis solution was added palladium-on-carbon catalyst (100 mg), and themixture was hydrogenated at 50 psi pressure overnight. The catalyst wasfiltered off and the ethanol evaporated to leave4-ethylamino-cyclohexanone 2', 2'-dimethyl trimethylene ketal as an oil(2.0 g).

This compound (0.80 g) was dissolved in formic acid (20 ml) and thesolution was heated to 90° C. for 1 hr. Formic acid was evaporated, andthe residue was partitioned between chloroform and 1M hydrochloric acid.The aqueous layer was evaporated to dryness to give4-ethylaminocyclohexanone (0.40 g).

A mixture of the above product (0.40 g) and 4-carboxamidophenylhydrazine hydrochloride (0.60 g) in glacial acetic acid (20 ml) washeated under reflux for 1 hr. The acid was evaporated in vacuo to anoil, which was purified by chromatography (SiO₂ ; CHCl₃ /10% NH₃ inMeOH) to give an oil (0.50 g). Part of this product (150 mg) wasdissolved in methanol and treated with oxalic acid. The solution wastreated with ether to give the title compound as a crystalline solid, mp165-170° C. (100 mg).

1H NMR 250 MHz, DMSO-d⁶ !δ 1.25 (3H, t), 1.81-2.05 (1H, m), 2.20-2.38(1H, m), 2.61-2.79 (1H, m), 2.79-2.94 (2H, m), 2.98-3.28 (3H, dd+s),3.41-3.60 (1H, m), 7.08 (1H, brd. s), 7.28 (1H, d), 7.60 (1H, d), 7.82(1H, brd. s), 8.00 (1H, s), 11.12 (1H, s).

Preparation 5

(±)-6-Carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole

A solution of(±)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazolehydrochloride salt (6.0g) in water (60 ml) at 68° C. was basified to pH10.5 with 5M aqueous sodium hydroxide. The resultant mixture wasextracted with butan-1-ol (30 ml, 15 ml). These extracts were combinedand evaporated to give the title compound as a dark oil (6.96 g)containing ca. 46% w/w butan-1-ol.

1H NMR 400 MHz, d⁶ -DMSO!δ 1.40-2.00 (1H,br), 1.62 (1H,m), 2.06 (1H,m),2.33 (1H,m) 2.39 (3H,s), 2.77 (3H,m), 2.97 (1H,dd), 7.02 (1H,s), 7.24(1H,d), 7.59 (1H,dd), 7.80 (1H,s), 7.99 (1H,d), 10.93 (1H,s) + peaks dueto butan-1-ol.

Preparation 6

4-Methiylaminocyclohexanone (2',2'-dimethyltrimethylene) ketalhydrochloride

1,4-Cyclohexanedione (mono-2'2'-dimethyltrimethylene) ketal (50g) wasdissolved in dry toluene (500 ml) in a flask fitted with a dry ice trapand flushed with nitrogen with stirring. Methylamine (47.0g) was thenadded dropwise to the reaction mixture, at 20° C. slowly to allowdissolution in the toluene. Molecular sieves (32.0 g) were then addedand the reaction mixture stirred at 20° C. under an air lock. Thereaction was complete after ca. 4 h (>97%). The sieves were thenfiltered off and the clear amber filtrate evaporated to a volume of 160ml. The concentrated solution of iminoketal was diluted with ethanol(340 ml) and degassed with argon. Palladium catalyst (palladium oncharcoal, 3.55 g) was added and the mixture hydrogenated at atmosphericpressure and 20° C. for 24 h. When hydrogen uptake was complete thereaction mixture was filtered through Celite and the Celite bed washedwith a little ethanol (2×25 ml). The solvent was then removed underreduced pressure to give the ketal amine as an amber oil. (49.12 g,92%).

The ketal amine (80 g, 0.375 Mol) was dissolved in isopropyl ether withstirring. A solution of HCl in isopropyl ether (prepared by bubbling aknown weight of gas into a known volume of solvent) was added dropwisecausing the formation of an immediate white precipitate, which becamevery thick as the addition was completed. The thick suspension wasstirred for a further 30 minutes, filtered off, and the product washedwith a little fresh isopropyl ether and then dried under vacuum to givethe title compound as a white, free flowing powder (84.01 g). 1H NMR: -270 MHz, CDCl₃ !δ 9.51 (2H,bs), 3.48 (4H,d), 3.00 (1H,m), 2.73 (3H,t),2.32 (2H,d), 2.15 (2H,d), 1.85, (2H,dq), 1.41 (2H,dt), 0.96 (6H,s).

Preparation 7

(±)-6-Carboxamide-3-methylamino-1,2,3,4-tetrahydrocarbazolehydrochloride

4-Aminobenzamide (3.0 g) was dissolved in 5N HCl (20 ml) cooled to -5 to0° C. with stirring and the mixture further cooled to around -15° C.Sodium nitrite (1.98 g) in water (4.4 ml) was added dropwise withstirring at such a rate that the temperature was maintained at between-10 to -15° C. The mixture was then stirred at around -8° C. for 30 min.Ice cold water (40 ml) was then added followed by solid sodiumdithionite (7.7 g) in a single portion, the means of cooling removed andthe mixture stirred at around 15° C. for 30 min. To the resulting yellowsuspension was added conc. HCl (30 ml) followed by4-methylaminocyclohexanone (2'2'-dimethyltrimethylene) ketalhydrochloride (5.488 g) and the mixture heated to around 70° C., notallowing the reaction temperature to rise above 75° C. After ca. 2 h,the reaction mixture was cooled to 20° C. and the dark solution thencarefully neutralised with caustic (aq., 40%) to pH 10 maintaining thetemperature between 15-20° C., whereupon a thick precipitate formed togive the title compound. The reaction mixture was then left to stirovernight and the precipitate filtered off and dried (3.88 g, 63%).

1H nmr 250 MHz, d₆ DMSO!δ=11.21 (1H,s), 8.06 (1H,s), 7.89 (1H,bs), 7.63(1H,d), 7.28 (1H,d), 7.10 (1H,bs), 3.50-3.15 (2H,m), 2.95-2.70 (3H,m),2.62 (3H,s), 2.33 (1H,m), 1.97 (1H,m).

Preparation 8

4-Methylaminocyclohexanone (2',2'-dimethyltrimethylene) ketalhydrochloride

1,4-Cyclohexanedione mono-2,2-dimethyltrimethylene ketal (20.0 g, 0.101mol) was dissolved in ethanol (200 ml) containing methylamine (8.0 g,0.258 mol). The resultant solution was hydrogenated at 30 psi over 10%Pd/C catalyst (2.0 g) for 4 hrs at room temperature. The reactionmixture was filtered through a celite pad and the filtrate evaporatedunder reduced pressure to give an oil (21.4 g).

The oil was dissolved in tetrahydrofuran (210 ml) and the resultantsolution cooled in an ice/water bath while conc.HCl (10.5 ml) was addedto the stirred solution in two portions such that the temperature didnot rise above 15° C. and then filtered. The solid was washed with THF(50 ml) and air dried overnight to give the title compound (22.80 g). mp245.1° C. (EtOH).

1H nmr (250 MHz, d₆ DMSO)δ 0.9 (s,6H), 1.3(q,2H), 1.45 (q,2H), 1.9(brd,2H), 2.25 (brd,2H), 2.5 (s,3H), 3.0 (m,1H), 3.5 (d,4H).

EXAMPLE 1

(+) and (-)-6-Carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazolehydrochloride

(a) To a stirred solution of(±)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazolehydrochloride (0.3 g) in propan-2-ol/saturated aqueous potassiumhydrogen carbonate (20:1 21 ml), di-tert-butyl dicarbonate (0.425 g) wasadded and stirring continued for 1 hour. The mixture was diluted withethyl acetate (50 ml) washed with water (2×20 ml), dried (MgSO₄) andsolvent removed at reduced pressure to give (±)3-N-tert-butoxycarbonyl-N-methylamino-6-carboxamido-1,2,3,4-tetrahydrocarbazole(0.36 g). ¹ H NMR (d₆ -DMSO) δ 1.47(s,9H), 1.84-2.08(m,2H),2.71-2.94(m,4H), 2.80(s,3H), 4.26(m,1H), 7.02(br.s,1H), 7.25(d,1H),7.57(d,1H), 7.76(br.s,1H), 7.97(s,1H) and 10.96(s,1H).

(b) The (+) and the (-) enantiomers of(±)-3-N-tert-butoxycarbonyl-N-methylamino-6-carboxamido-1,2,3,4-tetrahydrocarbazole(0.3 g) were separated by chiral HPLC: (chiralpak AD 20 mm column,hexane:ethanol 9:1 eluant).

Treatment of the first eluting enantiomer (0.02 g) with 3N aqueoushydrochloric acid/methanol 1:1 (4 ml) for 16 hours, filtration andremoval of solvent gave, after recrystallisation from methanol/diethylether, the (+) enantiomer of the title compound (0.009 g) m.p. 219-225°C., α!_(D) ²⁵° C. =+25.4 (methanol 0.063% w/v).

Treatment of the second eluting enantiomer (0.03 g) under similarconditions gave the (-) enantiomer of the title compound (0.02 g), m.p.219-225° C. α!_(D) ²⁵° C. =-23.3 (methanol 0.116% w/v).

EXAMPLE 2

(+)-6-Carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole

(a) To a solution of(±)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole (0.77 g)in dimethylformamide (70 ml), triethylamine (0.62 g) and benzylchloroformate (0.47 g) were added. The solution was stirred overnight,further triethylamine (0.27 g) and benzyl chloroformate (0.26 g) addedand the mixture stirred for 4 hours. The reaction mixture was pouredinto water (500 ml), and extracted with ethyl acetate (2×50 ml). Thecombined extracts were dried (MgSO₄) and solvent was removed at reducedpressure. The residue was recrystallised from methanol/water to give(±)-3-N-benzyloxycarbonyl-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole(0.62 g) m.p.103-110° C.

(b) The (+) and (-) enantiomers of(±)-3-N-benzyloxycarbonyl-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazolewere separated by chiral HPLC (OD column, eluant hexane/ethanol 4:1).

The first eluting enantiomer (0.23 g) m.p. 105-106° C., α!_(D) ²⁵° C.=+157.2. (ethanol, 0.39% w/v).

The second eluting enantiomer (0.23 g) m.p. 105-106° C., α!_(D) ²⁵° C.=-163.1 (ethanol, 0.23% w/v).

(c) A solution of(+)-3-N-benzyloxycarbonyl-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole(0.23 g) in ethanol (20 ml) containing 10% palladium/charcoal (0.23 g)was shaken under a hydrogen atmosphere (50 psi) for 3 hours. Catalystwas removed by filtration and solvent removed at reduced pressure togive the (+) enantiomer of the title compound (free base)as a foam m.p.98-102° C.,. α!_(D) ²⁵° C. =+61.2.

EXAMPLE 3

(+)-6-Carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazolecamphorsulphonate

To a solution of(±)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole (3 g) inmethanol (20 ml), a solution of (1S)-(+)-10-camphorsulphonic acid (2.86g) in methanol was added. Solvent was removed at reduced pressure andthe residue recrystallised ten times to give the (+) enantiomer of thetitle compound as the camphorsulphonate salt m.p. 177-180° C. This wastreated with 2 equivalents of triethylamine and 10 equivalents of2,3,4,6-tetra-o-acetyl-beta-D-glucopyranosylisothiocyanate indimethylformamide at room temperature for 30 minutes. Aliquots of thereaction mixture wre removed from the mixtue for HPLC analysis.Analytical HPLC of the2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosylthiourea derivative (C18Novapak, eluant methanol/50 mM NaH₂ PO₄ pH 2.9) gave the same retentiontime as the the same derivative prepared from the (+) enantiomer ofExample 1 and showed the material was 99% ee.

EXAMPLE 4

(+)-6-Carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole succinate(1:1)

(a) Benzaldehyde (10.6 g) was added to a suspension of(+)-3-amino-6-carboxamido-1,2,3,4-tetrahydrocarbazole (12.35 g) inmethanol (100 ml). The mixture was stirred for 1 hour, sodiumcyanoborohydride (9.3 g) added over 1 hour and the clear solutionstirred for 24 hours. The solution was cooled (ice bath) andformaldehyde (37% aqueous methanolic, 9:1 solution, 5.5 ml) added. After30 minutes stining at room temperature water (100 ml) was added,stirring continued for 30 minutes followed by extraction withdichloromethane (3×150 ml). The combined organic extracts were washedwith water (2×200 ml), dried (Na₂ SO₄), filtered and solvent removed atreduced pressure. The residue was column chromatographed (silica gel,dichloromethane-10% ethanol/dichloromethane) to give3-N-benzyl-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole(9.4 g) as a foam. The succinate salt (1:1) was recrystallised frommethanol m.p. 175-182° C.

¹ H NMR (d₆ -DMSO)δ 1.81-1.96(m,1H), 2.09-2.21(m,1H), 2.29(s,3H),2.44(s,4H), 2.66-3.11(m,5H), 3.76(q,2H), 7.05(br. s1H), 7.22-7.43(m,6H),7.59(d,1H), 7.79(br. s,1H), 8.03(s,1H), and 10.94(s,1H).

(b) To a solution of3-N-benzyl-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole(1.0 g) in ethanol (100 ml) containing succinic acid (0.39 g), Pearlmanscatalyst (1.0 g) was added and the mixture shaken under an atmosphere ofhydrogen at 45 psi and 50° C. for 2 hours. The mixture was filtered(celite pad) and the pad washed thoroughly with ethanol. The combinedfiltrate and washings were evaporated to dryness, co-evaporated withethanol (3×100 ml) and recrystallised from methanol to give the titlecompound (1:1) succinate salt!. m.p. 148-155° C.

¹ H NMR (d₆ -DMSO)δ 1.84(m,1H), 2.15-2.34(m,1H), 2.28(s,4H), 2.57(m,1H),2.61(s,3H), 2.83(m,2H), 3.13(dd,1H), 3.29(m,1H), 7.08(br s,1H),7.26(d,1H), 7.60(dd,1H), 7.82(br s,1H), 8.01(d,1H) and 11.08(s,1H).

EXAMPLE 5

(+)-6-Carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole

(a) To a solution of(+)-3-amino-6-carboxamido-1,2,3,4-tetrahydrocarbazole (5 g) in pyridine(150 ml), dicyclohexylcarbodiimide (4.13 g) was added followed by carbondisulphide (1.67 g). The solution was stirred for 1 hour, solventremoved at reduced pressure and the residue co-evaporated with toluene(3×100 ml). The residue was recrystallised from methanol to give6-carboxarnido-3-isothiocyanato-1,2,3,4-tetrahydrocarbazole (5.06 g)m.p.245-248° C.

(b) A solution of6carboxamido-3-isothiocyanato-1,2,3,4-tetrahydrocarbazole (0.25 g) inethanol (40 ml) was treated with sodium borohydride (0.17 g) in oneportion and stirred for 18 hours. Acetone (5 ml) was added the mixturestirred for a further 1 hour and solvent removed at reduced pressure.The residue was column chromatographed (basic alumina, 5%methanol/dichloromethane eluant) to give the title compound (0.11 g)having the same physico chemical characteristics as the product ofExample 2.

EXAMPLE 6

(+)- and (-)-6-Carboxamido-3-N-ethylamino-1,2,3,4-tetrahydrocarbazolehydrochloride

(a) From (±)-6-carboxamido-3-N-ethylamino-1,2,3,4-tetrahydrocarbazole(0.26 g), (±)-3-N-tertbutoxycarbonyl-N-ethylamino-6-carboxamido-1,2,3,4-tetrahydrocarbazole(0.27 g) isolated as an oil was prepared according to the procedure ofExample 1.

¹ H NMR (d₆ -DMSO) δ 1.1(t,3H), 1.23(s,9H), 1.92(m,1H), 2.09(m,1H),2.78-2.92(m,4H), 3.21-3.62(m,2H), 4.21(m,1H), 7.04(br.s,1H), 7.24(d,1H),7.58(d,1H), 7.76(br.s,1H), 7.99(s,1H) and 10.99(s,1H).

(b) From (±)-3-N-tertbutoxycarbonyl-3-N-ethylamino-1,2,3,4-tetrahydrocarbazole carbazole(0.25 g), the (+)- and the (-)-enantiomers of 3-N-tertbutoxycarbonyl-3-N-ethylamino-1,2,3,4-tetrahydrocarbazole were preparedby chiral HPLC (chiralcel OD 4.67 mm, eluant hexane/ethanol 92/8).

Treatment of the enantiomer eluting first, (0.06 g) α!_(D) ²⁵° C.=+108.2 (ethanol 0.9%w/v) with hydrochloric acid/methanol according tothe method of Example 1 gave(+)-6-carboxamido-N-ethylamino-1,2,3,4-tetrahydrocarbazole hydrochloride(0.04 g) m.p. 211-221° C. α!_(D) ²⁵° C. =+37.2 (methanol, 0.12% w/v).

Treatment of the second eluting enantiomer (80 mg) α!_(D) ²⁵° C. =-103.5(ethanol, 0.19% w/v) with hydrochloric acid/methanol according to themethod of Example 1 gave(-)-6-carboxamido-3-N-ethylamino-1,2,3,4-tetrahydrocarbazolehydrochloride (0.05 g) m.p. 211-221° C. after recrystallisation frommethanol/diethyl ether α!_(D) ²⁵° C. =-33.6 (methanol, 0.11 % w/v).

EXAMPLE 7

(+)-6-Carboxamido-3-N-ethylamino-1,2,3,4-tetrahydrocarbazole succinate(1:1)

(a) From (+)-3-amino-6-carboxamido-1,2,3,4-tetrahydrocarbazole (1.15 g),(+)-3-N-benzyl-N-ethylamino-6-carboxamido-1,2,3,4-tetrahydrocarbazole(1.26 g) was obtained according to the procedure of Example 4 replacingformaldehyde with acetaldehyde (0.44 g). The succinate salt (1:1) wasprepared by addition of succinic acid (0.4 g) to the free base (1.08 g)and recrystallisation from propan-2-ol m.p. 130-140° C.

¹ H NMR (d₆ -DMSO) δ 1.05(t,3H), 1.85(m,1H), 2.10(m,1H), 2.40(s,4H),2.58-2.91(m,5H), 3.06(m,1H), 3.77(q,2H), 7.03(br.s,1H), 7.17-7.47(m,5H),7.58(d,1H), 7.78(br.s,1H), 8.00(s,1H), 10.90(s,1H) and 12.28(br.s2H).

(b) Recrystallisation of(+)-3-N-benzyl-N-ethylamino-6-carboxamido-1,2,3,4-tetrahydrocarbazolesuccinate (1.36 g), from methanol, according to the procedure of Example4 gave the title compound (1.04 g) m.p. 165-167° C.

1H NMR (d6-DMSO) δ 1.19(t,3H), 1.86(m,1H), 2.23(m,1H), 2.30(s,4H),2.62(m1H), 2.85(m,2H), 3.02(q,2H), 3.14(m,1H), 3.38(m,1H),7.08(br.s,1H), 7.26(d,1H), 7.59(d,1H), 7.80(br.s,₁ H), 8.00(s,1H) and11.08(s,1H).

EXAMPLE 8

(+)-6-Carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole L(+)-tartrate salt (1:1)

To a hot solution of(+)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole (0.25 g)in methanol/water (11:1, 24 ml) L (+)-tartaric acid (0.15 g) was addedand the solution allowed to stand for 3 hours. The crystalline titlecompound (0.30 g) was isolated by filtration. m.p. 195-197° C.

¹ H NMR (d₆ -DMSO) δ 1.92(m,1H), 2.25(m,1H), 2.67(s,3H), 2.68(m,1H),2.84(m,2H), 3.17(dd,1H), 3.43(m,1H), 3.87(s,2H), 7.07(br.s,1H),7.27(d,1H), 7.61(d,1H), 7.82(br.s,1H), 8.01(s,1H) and 11.11(s,1H).

EXAMPLE 9

(+)-6-Carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole D(-)-tartrate salt (1:1)

To a hot solution of(+)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole (0.25 g)in methanol (9 ml) D (-)-tartaric acid (0.15 g) was added and thesolution allowed to stand for 3 hours. The crystalline title compound(0.32 g) was isolated by filtration m.p. softens above 147° C. ¹ H NMR(d₆ -DMSO)δ 1.92(m,1H), 2.25(m,1H), 2.67(s,3H), 2.84(m,2H), 3.17(dd,1H),3.43(m,1H), 3.87(s,2H), 7.07(br.s,1H), 7.27(d,1H), 7.61 (d,1H),7.82(br.s,1H), 8.02(s,1H) and 11.09(s,1H).

EXAMPLE 10

(+)-6-Carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazolehemisuccinate (2:1)

To a hot solution of(+)-6-carboxamido-3-N-methylamino-1,2,3,4tetrahydrocarbazole (0.30 g) inpropan-2-ol was added succinic acid (0.07 g) and the solution allowed tostand for 3 hours. The title compound (0.21 g) was isolated byfiltration. m.p. 220-235° C.

¹ H NMR (d₆ -DMSO)δ 1.77(m,1H), 2.14(m,1H), 2.26(s,2H), 2.54(s,3H),2.55(m,1H), 2.79(m;2H), 3.10(dd,1H), 3.43(m,1H), 7.06(br.s,1H),7.25(d,1H), 7.59(d,1H), 7.82(br.s,1H), 7.99(s,1H) and 11.01(s,1H).

EXAMPLE 11

(+)-6-Carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazolemethanesulphonate

To a hot solution of(+)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole (0.30 g)in propan-2-ol/ethyl acetate methanesulphonic acid (0.12 g) was addedand the solution allowed to stand for 3 hours. The title compound (0.33g) was isolated as a gum.

¹ H NMR (d₆ -DMSO)δ 1.93(m,1H), 2.25(m,1H), 2.35(s,3H), 2.70(m,4H),2.86(m,2H), 3.10(dd,1H), 3.50(m,1H), 7.11(br.s,1H), 7.27(d,1H),7.61(d,1H), 7.82(br.s,1H), 8.02(s,1H), 8.65(br.s,2H) and 11.12(s,1H).

EXAMPLE 12

(+)-6-Carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazolehydrobromide

Hydrogen bromide gas was passed through a solution of(+)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole (0.30 g)in ethanol(50 ml) for 15 seconds. After 30 minutes the title compound(0.03 g) m.p. 205-208° C. was separated by filtration and washed withethanol.

¹ H NMR (d₆ -DMSO) δ 1.94(m,1H), 2.25(m,1H), 2.26(s,2H), 2.70(m,4H),2.85(m,2H), 3.17(dd,1H), 7.10(br.s,1H), 7.27(d,1H), 7.61(d,1H),7.82(br.s,1H), 8.02(s,1H) 8.67(br.s,2H) and 11.01(s,1H).

EXAMPLE 13

a)(+)-6-Carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole-R-2-pyrrolidone-5-carboxylicacid salt

To a solution of(±)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole (6.96 gcontaining ca. 46% w/w butan-1-ol, prepared as in Preparation 5) inethanol (50 ml), stirred at ambient temperature, was added a solution ofR-2-pyrrolidone-5-carboxylic acid (1.00 g, e.e. >99%) in hot ethanol (33ml). The resultant mixture was stirred at ambient temperature for 40 h.The crystalline product was filtered off under nitrogen, washed with asmall volume of ethanol, then dried in vacuo at 60° C. (Yield=2.63 g).

This product was dissolved in water (2.6 ml), and the solution was thendiluted with ethanol (130 ml) and stirred at ambient temperature for 40h. The crystalline product was filtered off, washed and dried as before.(Yield=1.72 g).

This product was recrystallised from ethanol (90 ml)/water (1.8 ml) asdescribed above to give the title compound (1.44 g; e.e.=>99%). ¹ H NMR250 MHz, d₆ -DMSO! δ 1.90 (2H,m), 2.06 (2H,m), 2.19 (2H,m), 2.57 (3H,s),2.62 (1H,m), 2.82 (2H,m), 3.15 (2H,m), 3.80 (1H,dd), 7.07 (1H,s), 7.26(1H,d), 7.59 (1H,s), 7.62 (1H,s), 7.84 (1H,s), 8.00 (1H,s), 11.10(1H,s)+peaks due to ethanol.

b) (+)-6-Carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazolesuccinate salt, monohydrate

A solution of(+)-6carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazoleR-2-pyrrolidone-5-carboxylic acid salt (1.34 g) in water (5.4 ml) wasbasified to pH 13.2 with 5M aqueous sodium hydroxide. The resultantmixture was extracted with butan-1-ol (5.4 ml). This extract wasevaporated to give(+)-6-carboxamido-3-N-methylamino-1,2,3,4-tetrahydrocarbazole as anoil/solid (735 mg) containing ca. 2% w/w butan-1-ol.

A portion of this product (232 mg) was dissolved in ethanol (1.45 ml).This solution was filtered, and added dropwise to a stirred solution ofsuccinic acid (110 mg) in ethanol (1.45 ml)/water (0.48 ml). The mixturewas seeded before the addition was complete. Stirring was continued for30 min at ambient.temperature, then 30 min at 0° C. The crystallineproduct was filtered off, washed with a small volume of ethanol, thendried in vacuo at 60° C. Yield=233 mg.

¹ H NMR 250 MHz, d₆ -DMSO! δ 1.87 (1H,m), 2.25 (1H,m), 2.29 (4H,s), 2.62(3H,s), 2.65 (1H,m), 2.83 (2H,m), 3.15 (1H,dd), 3.34 (1H,m), 7.09(1H,s), 7.27 (1H,d), 7.61 (1H,dd), 7.84 (1H,s), 8.02 (1H,s), 11.10(1H,s).

We claim:
 1. A process for preparing an enantiomer of formula (I)##STR7## wherein R⁴ is methyl or ethyl, or a salt, solvate or hydratethereof which comprises alkylating a (+) or (-) enantiomer of3-amino-6-carboxamido-1,2,3,4-tetrahydrocarbazole or a salt thereof,followed if necessary or desired by removal of any N-protecting group,conversion of a salt into a free base and/or salt formation.